The invention relates generally to methods of physical vapor deposition of copper onto a substrate.
In the formation of integrated circuits (IC), thin films containing metal and metalloid elements are deposited upon the surface of a semiconductor substrate or wafer. The films provide conductive and ohmic contacts in the circuits and between the various devices of an IC. For example, a thin film of a desired metal might be applied to the exposed surface of a contact or via in a semiconductor substrate. The film, passing through the insulative layers of the substrate, provides plugs of conductive material for the purpose of making interconnections across the insulating layers.
One well known process for depositing a thin metal film is by chemical vapor deposition (CVD). In CVD, reactant or deposition gas precursors are pumped
One well known process for depositing a thin metal film is by chemical vapor deposition (CVD). In CVD, reactant or deposition gas precursors are pumped into proximity to a target and substrate inside a reaction chamber. The precursors are activated using either thermal energy or electrical energy, and subsequently undergo chemical reactions at the surface of the target and substrate. This results in one or more reaction by-products, which are deposited on the exposed substrate or wafer surface to form a film.
CVD of copper provides the desirable property of high step coverage of the substrate, that is, a high ratio of the coating thickness at the bottom of a feature such as a trench or via, relative to the thickness of the coating on the top surface of the substrate adjacent the feature. CVD of copper, however, suffers from several difficulties and limitations. Adhesion of films deposited by CVD on most substrates utilized for copper technologies is difficult because most copper precursors do not sufficiently nucleate. As a result, nucleation is uneven as well as spotty, leading to poor non-conformal film growth with poor grain size and orientation control. Deposition of copper with most precursors is also difficult to control because of the poor stability of the precursor sources as well as the frequent early decomposition of the precursor in the delivery device.
It has been shown that copper deposited by CVD using a hexafluoroacetylacetonate (hfac) type of copper precursor results in conformal film growth over topography with about 100% step coverage. On the other hand, it is also known that in most cases deposition is gas feed limited, which usually results in very poor conformality due to depletion of the precursor in the trench or via. These factors suggest that somehow the hfac type of precursor and other copper precursors have a unique ability to uniformly coat the topography of a device, regardless of what precursor concentrations or partial pressure exists.
Physical vapor deposition (PVD), whereby electrical energy creates a vapor of particles to deposit onto a substrate, provides several desirable properties when copper is deposited. Copper deposited by PVD onto commonly used substrates shows very good adhesion, and good grain size and orientation, which are key to reliable copper metallization schemes. However, PVD of copper has the disadvantage that, while PVD can be highly directional with generous amounts of copper on the top and bottom horizontal surfaces, there is relatively little copper deposited on the vertical wall surface of a feature, such as a trench or via.
A PVD method for depositing copper onto a substrate is desirable. Such a method will provide the good adhesion and good grain size and orientation advantages of PVD.
The invention is directed to a method to redistribute solid copper deposited by PVD on a wafer topography, to result in enhanced uniform coverage of copper. To this end, and in accordance with the principles of the present invention, the deposited copper is solubilized in a fluid under solubilizing-promoting conditions in the reaction chamber, transported and redeposited. These steps may be performed for as many times as necessary to achieve redistribution. The solubilizing fluid may be a gas or a liquid. The method may further include supplying an electric field to the wafer. Copper may be redeposited by changing the temperature and/or the pressure in the reaction chamber.
The invention is further directed to a method of redistributing copper deposited on a wafer surface having a topography. At least a part of the surface copper is volatilized. A concentration of the volatilized copper is maintained to diffuse into the topography for redeposition. Volatilizing may be obtained by flowing an etching agent above the wafer. The concentration of the removed copper may be maintained high by a copper plate positioned adjacent the wafer, and the temperature of the plate and chamber may be higher than the temperature of the wafer.
The invention improves the uniformity of thickness of the resulting copper film. These and other objects and advantages of the present invention shall be made apparent from the accompanying description and examples thereof.